Abstract: Objective　To investigate the effects and underlying mechanisms of the combination of STAT3 inhibitors (Stattic and S3I-201) and nicotinamide adenine dinucleotide (NAD) precursor nicotinamide on the proliferation of hepatocarcinoma HepG2 cells. Methods　Hepatocarcinoma HepG2 cells were treated with STAT3 inhibitor, nicotinamide and their combination. Cell counting, Western blot assay and qPCR were used to examine the effects of drugs on cell proliferation, STAT3 expression and mRNA expression levels of STAT3 downstream target genes (SNAIL1, VEGFA and ZEB1), cell proliferation (MCM7, MKI67 and MYC), apoptosis (BCL-2, MCL-1 and BAX), epithelial-mesenchymal transformation (TJP1 and SMAD3), and glucose metabolism (HK2, PFKL, PKM, GLUT1 and LDHA)-related genes. Results　Both STAT3 inhibitor and nicotinamide treatment can decrease the phosphorylation level of STAT3, inhibit cell proliferation, downregulate the expression levels of genes related to cell proliferation, anti-apoptosis, EMT, and glucose metabolism, and upregulate the expression levels of genes related to pro-apoptosis. In addition, the combination of drugs showed a more significant effect on the phosphorylation level of STAT3, cell proliferation and expression levels of the above-mentioned cellular process-related genes. Conclusion　STAT3 inhibitor and nicotinamide can inhibit the proliferation of hepatocarcinoma cells, and the combined effect is more significant. This inhibition may be related to the promotion of apoptosis, the inhibition of EMT and glycolysis.

Key words: carcinoma, hepatocellular, HepG2 cells, STAT3 transcription factor, nicotinamide, cell proliferation, apoptosis, epithelial-mesenchymal transition, glycolysis